Update visual regression test action

 - Updated to meet the GOV.UK conventions for GitHub Actions [1]
 - Updated Yarn caching of the node modules to have the folder cached, as the
   place where Yarn caches the dependencies depends on the operating system
   and version of Yarn [2]
 - Replaced GitHub's Ruby setup with `ruby/setup-ruby`, as that can read the
   `.ruby-version` instead of setting the version in the Action's config file.

[1] https://docs.publishing.service.gov.uk/manual/test-and-build-a-project-with-github-actions.html
[2] https://github.com/actions/cache/blob/8b407f7777cf8b88a75f09b87331f535315cf621/examples.md#node---yarn

.github/workflows/visual-regression-tests.yml

@@ -1,44 +1,40 @@
-name: "Visual regression test"
-
 on:
   push:
     branches:
       - main
       - master
   pull_request:
     types:
-      - "ready_for_review"
+      - ready_for_review
 
 jobs:
   visual-regression-test-components:
-    runs-on: "ubuntu-latest"
+    runs-on: ubuntu-latest
     steps:
-      - uses: "actions/checkout@v2"
-      - uses: "actions/setup-ruby@v1"
-        with:
-          ruby-version: "2.7"
-      - uses: "actions/[email protected]"
+      - uses: actions/checkout@v2
+      - uses: ruby/setup-ruby@v1
+      - uses: actions/setup-node@v1
         with:
           node-version: "14"
-      - name: "Cache node modules"
-        uses: "actions/cache@v2.1.3"
+      - name: Check for cached Ruby gems
+        uses: actions/cache@v2
         with:
-          path: "~/.npm"
-          key: "${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}"
-          restore-keys: "${{ runner.os }}-node-"
-      - name: "Cache Ruby gems"
-        uses: "actions/[email protected]"
+          path: vendor/bundle
+          key: ${{ runner.os }}-gems-${{ hashFiles('**/Gemfile.lock') }}
+          restore-keys: ${{ runner.os }}-gems-
+      - name: Get Yarn cache directory path
+        id: yarn-cache-directory-path
+        run: echo "::set-output name=dir::$(yarn cache dir)"
+      - name: Check for cached Yarn dependencies
+        uses: actions/cache@v2
         with:
-          path: "vendor/bundle"
-          key: "${{ runner.os }}-gems-${{ hashFiles('**/Gemfile.lock') }}"
-          restore-keys: "${{ runner.os }}-gems-"
-      - name: "Bundle and yarn install"
-        run: |
-          bundle config path tmp/bundle
-          bundle install --jobs 4 --retry 3
-          yarn install --frozen-lockfile
-      - uses: "percy/[email protected]"
+          path: ${{ steps.yarn-cache-directory-path.outputs.dir }}
+          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
+          restore-keys: ${{ runner.os }}-yarn-
+      - run: bundle install --jobs 4 --retry 3 --path vendor/bundle
+      - run: yarn install --frozen-lockfile
+      - uses: percy/[email protected]
         with:
-          command: "bundle exec rspec ./spec/visual_regression_tests/all_components.rb"
+          command: bundle exec rspec ./spec/visual_regression_tests/all_components.rb
         env:
-          PERCY_TOKEN: "${{ secrets.PERCY_TOKEN }}"
+          PERCY_TOKEN: ${{ secrets.PERCY_TOKEN }}